1. Field of the Invention
This invention relates to small-sized relays. More particularly, this invention relates to an improved small-sized relay hermetically sealed or enclosed which is provided in its cover portion with a plurality of holes of very small diameter permitting a flow of gas molecules therethrough but not permitting the flow of dust particles and liquid molecules therethrough, and relates also to a method for fabricating such a relay.
2. Description of the Prior Art
In a small-sized relay, it has been typical to enclose its relay mechanism by an enclosure or cover for preventing intrusion or permeation of dust and moisture from the exterior, as disclosed in, for example, copending United States patent application Ser. No. 298,433 filed by the same inventor on Sept. 1, 1981. The object of the copending patent application is to isolate the internal relay mechanism from the ambient atmosphere thereby protecting the parts including the relay contacts from being affected by various external conditions encountered by the relay in the environment in which the relay is used.
However, in such a small-sized relay of the enclosed type, an increase in the frequency of operation of the relay contacts has sometimes resulted in the tendency of rusting of the parts including the contacts and yoke in the relay mechanism, and the formation of rust has provided a principal source of degradation of the relay or misfunction of the relay contacts.
In an attempt to obviate such a defect, a proposal has been made in which a vent hole is formed in the cover portion of the relay, as will be described later with reference to FIG. 1. However, a small-sized relay of the type considered herein is frequently mounted on a printed circuit board. In such a case, soldering is commonly employed for establishing predetermined electrical connections between the relay and the printed circuit board after the relay is mounted in a predetermined position on the printed circuit board, and it is necessary to wash away the soldering flux after the step of soldering. In this washing step, washing with the washing solution has been applied to the soldered area only of the relay provided with such a vent hole in the cover so that the washing solution may not flow into the relay through the vent hole formed in the cover. Therefore, the above proposal has still been defective in that a limited portion only of the relay can be washed. One of the attempts for obviating such a defect is disclosed in Japanese Patent Publication No. 1852/1982 published Jan. 13, 1982. According to the disclosure of this patent publication, a portion of the cover of a relay of the enclosed type is removed to form a venting structure in the cover after the relay has been mounted on a printed circuit board by soldering and then washed with a washing solution. The above-described method is therefore advantageous in that there is no possibility of flowing of the washing solution into the relay although the relay is bodily immersed in the washing solution for washing of the whole including its soldered area.
However, the method disclosed in Japanese Patent Publication No. 1852/1982 cited above has still been defective in that, because of the necessity for formation of a venting structure in the cover of each individual relay after the steps of mounting it on a printed circuit board and washing it with a washing solution, considerable man-hours are required for the fabrication.